Thallus development

In studies of members of the Trypetheliaceae growing on thin-barked trees, Johnson (1940) found that the entire thallus development occurred within the periderm, from initial lichenization with Trentepohlia filaments (which had already penetrated the bark 8-10 cell layers deep) to complete perithecial maturity. 

Schoenwaelder MEA (2002b) Physode distribution and the effects of Thallus Sunburn in Hormosira banksii (Fucales, Phaeophyceae). Bot Mar 45 262-266 Schoenwaelder MAE, Wiencke C, Clayton MN, Glombitza KW (2003) The effect of elevated UV radiation on Fucus spp. (Fucales, Phaeophyta) zygote and embryo development. Plant Biol 5 366-377... 

Eucarpic sterile and fertile portions of thallus distinct from early stages or developed from specialized regions. 

Multicellular organisms sometimes show marked differences in the extent to which surface phosphatases are developed on different parts of the thallus. This is most striking in taxa forming multicellular hairs (see below), which enhance the surface-to-volume ratio. However, in general, the larger the organism, the lower is the value for this ratio Hernandez et al. (1999) assessed the implication of this for seaweeds. 

Verma N (2011) Studies on antioxidant activities of some lichen metabolites developed in-vitro, Shodh ganga, Indian ETD Repository, Issue 2 Sept 2011 Verma N, Behera BC, Makhija U (2008a) Antioxidant and hepatoprotective activity of a lichen Usnea ghattensis in-vitro. Appl Biochem Biotechnol 151 167-181 Verma N, Behera BC, Sonone A et al (2008b) Cell aggregates derived from natural lichen thallus fragments antioxidant activities of lichen metabolites developed in-vitro. Nat Prod Commun 3 1911-1918... 

The tissues of the thallus consist of certain cell types, which are derived from the simple cells of the fungal hyphae. For a better understanding of the habit and structure of the lichen thallus it is, therefore, convenient to describe the original fungal cell and to follow its development into the specialized cells of which the various tissues and thalli are composed. 

The structure and development of the tissues depends on the form of the cells and on the particular type of contact between them. This is achieved either by the mutual adherence of the cell walls, by the formation of anastomoses, or by the gelatinization of the cell walls. Other important factors are the direction of growth and the orientation of the hyphae to the surface of the thallus and to each other (Figs. 5-8). 

Most lichens are more complex in structure. The algae are restricted to a particular layer in the thallus and besides the algal zone there is at least one other defined layer, the medulla, which contains no algae. Other layers, a cortex for example, may also be developed. These thalli with a stratified organization are called heteromerous (Fig. 93). 

The development of the thallus verticalis in Stereocaulon (Fig. 80) and Pilophorus (Fig. 81) is different. A part of a squamule of the thallus horizon-talis or a complete granule of the thallus grows vertically upwards and develops into a simple or branched more or less erect thallus verticalis. The primordium of the fruiting body is formed only at the top of this stalk. The generative tissue builds only the ascocarp while the thallus verticalis is differentiated from vegetative thallus tissue. This kind of stipe is called a pseudopodetium. 

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